Electrostatic machine system and method of operation

ABSTRACT

An illustrative electrostatic machine includes a shaft that is configured to rotate about an axis, a rotor electrode, and a stator electrode. The rotor electrode and the stator electrode are separated by a gap and form a capacitor. The rotor electrode is fixed to the shaft. The electrostatic machine can also include a housing that is configured to enclose the rotor electrode, the stator electrode, and at least a portion of the shaft. The stator electrode is fixed to the housing. A dielectric fluid fills a void defined by the housing, the rotor electrode, and the stator electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 62/059,903, filed Oct. 5, 2014, which is incorporatedherein by reference in its entirety.

STATEMENT OF GOVERNMENT RIGHTS

The present disclosure was made with government support under IIP1345755 awarded by the National Science Foundation. The government hascertain rights in the invention.

FIELD

The present technology generally relates to electrostatic rotatingmachines and a fill fluid for such machines. More particularly, thetechnology relates to machines such as motors and generators that havecapacitance plates separated by a fluid, such as a dielectric fluid.

SUMMARY

An illustrative electrostatic machine includes a shaft that isconfigured to rotate about an axis, a rotor electrode, and a statorelectrode. The rotor electrode and the stator electrode are separated bya gap and form a capacitor. The rotor electrode is fixed to the shaft.The electrostatic machine can also include a housing that is configuredto enclose the rotor electrode, the stator electrode, and at least aportion of the shaft. The stator electrode is fixed to the housing. Adielectric fluid fills a void defined by the housing, the rotorelectrode, and the stator electrode. The dielectric fluid comprises atleast one of an acyclic structure or a cyclic structure.

In some embodiments, the dielectric fluid is a carbonate (i.e.—OC(O)O—). In some embodiments, the dielectric fluid includes anaromatic structure in which a nitrogen atom is present at a firstposition in a ring of the aromatic structure and at least one nitrile(CN) group is a substituent at a second position. In some embodiments,the dielectric fluid includes 2-pyridinecarbonitrile.

In some embodiments, the dielectric fluid comprises a cyclic structureand includes a chemical functional group represented as —OC(O)N—. Insome embodiments, the dielectric fluid includes3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone,3-methyl-1,3-oxazinan-2-one, or a mixture of any two or more thereof. Insome embodiments, the dielectric fluid includes an acyclic, fluorinatedhydrocarbon. In some embodiments, the dielectric fluid includes C₅H₂F₁₀.In some embodiments, the dielectric fluid is an organic compound havinga sulfonyl moiety (—S(O)₂—). In some embodiments, the dielectric fluidincludes dimethyl sulfone, sulfolane, or a mixture thereof.

In some embodiments, the dielectric fluid includes ethylene carbonate,dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropylcarbonate, propylene carbonate, methyl butyrate, γ-butyrolactone,N-methylpyrrolidinone, vinylene carbonate, dioxolane, 6-butyrolactone,or diethyl ether. In some embodiments, the dielectric fluid includespropylene carbonate having a purity of greater than 99%. In someembodiments, the rotor electrode and the stator electrode each comprisea passivation layer formed using a second dielectric in the gap betweenthe rotor electrode and the stator electrode. The second dielectricfluid comprises less than 99 wt % propylene carbonate. In someembodiments, the second dielectric fluid includes 93.8 vol % propylenecarbonate, 6 vol % ethylene sulfite, and 0.2 vol % water. In someembodiments, a voltage is applied across the capacitor, and wherein thedielectric fluid forms a passivation layer on a surface of the rotorelectrode and on a surface of the stator electrode.

In some embodiments, the electrostatic machine can further include acurrent sourced inverter that is configured to convert direct currentpower into alternating current power via a plurality of switches. Thecurrent sourced inverter is configured to provide the alternatingcurrent power across the rotor electrode and the stator electrode. Nopassive electrical components are electrically connected between therotor electrode, the stator electrode, and the plurality of switches.

In some embodiments, the electrostatic machine can further include avoltage sourced inverter that is configured to convert direct currentpower into alternating current power via a plurality of switches. Aplurality of inductors are electrically connected between the rotorelectrode, the stator electrode, and the plurality of switches.

In some embodiments, the rotor electrode comprises a rotor plate, thestator electrode comprises a stator plate, and the rotor plate and thestator plate are parallel. The rotor plate comprises a plurality ofteeth around a periphery of the rotor plate. The stator plate comprisesan annulus with a plurality of teeth extending from an insidecircumference of the annulus. The teeth of the rotor plate and the teethof the stator plate form the capacitor. In some embodiments, the housingcomprises at least one of polypropylene, chemical resistant acetal,ultra-high-molecular-weight (UHMW) polyethylene, andpolytetrafluoroethylene (PTFE).

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the following drawings and thedetailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B illustrate cross-sectional views of some shapes of arotor disk or plate in accordance with illustrative embodiments.

FIGS. 2A and 2B illustrate cross-sectional views of some shapes of astator ring/plate in accordance with illustrative embodiments.

FIG. 3A is a diagram illustrating the capacitive relationship between arotor and stators in accordance with an illustrative embodiment.

FIG. 3B illustrates the positional relation of rotors and stators inaccordance with an illustrative embodiment.

FIG. 3C is an illustration of an exploded view of a configuration ofstators and rotors in accordance with an illustrative embodiment.

FIG. 4A illustrates a rotor with radial veins in accordance with anillustrative embodiment.

FIG. 4B illustrates a stator with radial veins in accordance with anillustrative embodiment.

FIG. 4C is an illustration of an exploded view of a configuration ofstators and rotors with radial veins in accordance with an illustrativeembodiment.

FIGS. 5A and 5B are plots of the capacitance between a stator and arotor versus angular position in accordance with illustrativeembodiments.

FIG. 6 is a cross-sectional view of an electrostatic machine inaccordance with an illustrative embodiment.

FIGS. 7A and 7B illustrate exterior views of an electrostatic machine inaccordance with an illustrative embodiment.

FIG. 8 is an illustration of an exploded view of some components of anelectrostatic machine in accordance with an illustrative embodiment.

FIGS. 9A and 9B are circuit diagrams of a three-phase inverter and athree-phase machine in accordance with illustrative embodiments.

FIGS. 9C and 9D are circuit diagrams of a single-phase of a three-phaseinverter in accordance with illustrative embodiments.

FIGS. 9E and 9F are circuit diagrams of a single-phase buck or boostconverter of a three-phase inverter powering a single-phase of athree-phase machine in accordance with illustrative embodiments.

FIGS. 10A and 10B are diagrams of some examples of creating switches inaccordance with illustrative embodiments.

FIGS. 11A and 11B are block diagrams of a capacitive machine drivecontrol system in accordance with illustrative embodiments.

FIG. 11C is a block diagram of a circuit architecture for powering anelectrostatic machine in accordance with an illustrative embodiment.

FIG. 12 is a block diagram of a controller in accordance with anillustrative embodiment.

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. Understanding thatthese drawings depict only several embodiments in accordance with thedisclosure and are, therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe figures, can be arranged, substituted, combined, and designed in awide variety of different configurations, all of which are explicitlycontemplated and make part of this disclosure.

Electrostatic machinery include electric motors and generators thatconvert power between mechanical (e.g., kinetic) and electrical formsusing electric field torque mechanisms. In general, electrostaticmachines use capacitive principles (as opposed to inductive principlesused in induction, permanent magnet, and reluctance machines). In someembodiments, electrostatic machines can use circular plates located inclose proximity to one another to create a capacitance between theplates. In some embodiments, the plates can alternate between rotorplates and stator plates. Rotor plates can be plates that rotate with ashaft of the motor and/or generator and can be analogous to an armatureof an induction or reluctance motor. Stator plates can remain stationarywith respect to a housing or enclosure of the motor and/or generator.

In general, energy storage systems (e.g., capacitors) can naturallyarrange themselves to be in a minimal energy state. In the case ofvariable capacitance machines (and other electrostatic machines),surfaces affixed to a shaft (e.g., rotor plates) can form a capacitancewith surfaces affixed to a housing (e.g., stator plates). When voltageis applied across rotor plates and the stator plates, an electric fielddevelops between the rotor plates and the stator plates and can exert aforce (e.g., torque) on the surfaces of the rotor plates and the statorplates in a direction that will align the rotor plates and the statorplates in a position with a minimal energy state.

Some electrostatic machines can produce a large electric field across apair of electrodes (e.g., stator plates and rotor plates) to generatesufficient torque for practical applications. Air has a low breakdownvoltage (e.g., is prone to arcing). Thus, in some embodiments, adielectric fluid can be located between the electrodes (e.g., statorplates and electrode plates) and a high electric field can be maintainedwithout arcing between the electrodes.

Torque generation in an electrostatic machine can be directly related tothe normal and shear forces between the electrodes. The electrostaticnormal force density F between the electrodes can be estimated usingCoulomb's law:F=(½)∈₀ ∈E ²where ∈₀ is the vacuum permittivity of the medium between the electrodesin farads per meter (F/m), ∈ is the static permittivity of the mediumbetween the electrodes, and E is the electric field in volts per meter(V/m). The force density can be optimized by using a medium between theelectrodes that has a high permittivity and by applying a large electricfield across the electrodes without arcing between the electrodes. Insome embodiments, the medium can be in a liquid state. In mostinstances, liquids can have a higher relative permittivity than gases.Other considerations can be taken into account when choosing a fillmedium. For example, the ionic conductivity of the medium can be low.Ionic contaminants can facilitate electron transport between theelectrodes, resulting in premature dielectric breakdown and, thus,inhibiting application of a high electric field. Liquid viscosity can below thereby minimizing drag on moving parts. In some instances, a fluidwith high permittivity and low conductivity, which can be locatedbetween rotor plates and stator plates, can be generally referred to asa dielectric fluid. However, in other instances, a fluid with lowrelative permittivity can be used. For example, in some embodiments,acyclic carbonates and/or ethers can be used, which may have a lowrelative permittivity but may have other desirable characteristics.

Electrostatic machines may be divided into six categories: electrostaticinduction machines, variable capacitance/elastance machines, synchronouselectrostatic machines, direct current (DC) electrostatic machines,electrostatic hysteresis synchronous machines, and corona machines. Insome instances, a particular machine may fall into one or more of thecategories. Such categories are not exclusive, and additional categoriesmay exist. The use of such categories is used for explanatory purposesonly, and is not meant to be limiting. The following descriptions of thecategories explain the general, underlying principles used in themachines of each category.

Electrostatic induction machines can use electrodes on a stator toproduce a traveling potential wave. The potential wave can induce acharge distribution on a rotor adjacent to the stator. The rotor surfacecan be continuous and, in at least some instances, does not exhibitcapacitive saliency. When the stator and the rotor have a net velocitybetween them (e.g., the stator and the rotor move relative to oneanother), a tangential component of the electrical field in a gapbetween the stator and the rotor can exist in the gap. The tangentialcomponent can result in a coulomb force on the rotor charge. Therelative velocity between the stator and rotor can be referred to as theslip speed. In some aspects, electrostatic induction machines can beconsidered to be analogous to magnetic induction machines that use aversion of slip.

Variable capacitance machines can be referred to as elastance machines.Variable capacitance machines can minimize elastance (or maximizecapacitance) to create torque. When a voltage is applied across statorelectrodes and rotor electrodes, the rotor electrodes can experience atorque in a direction to align the rotor to be in a minimum energy statewith respect to the stator. The torque can be proportional to the changein capacitance per unit angle (e.g., dC/dθ). Variable capacitancemachines can be designed to maximize the change in capacitance over arotational angle. The manner in which the capacitance varies with anglemay be synchronous (e.g., sinusoidal) or switched (e.g., trapezoidal).In some aspects, variable capacitance machines can be considered to beanalogous to magnetism based variable reluctance machines.

Synchronous electrostatic machines can have a rotor with a fixed DCcharge distribution across the rotor. The DC charge distribution canprovide a DC electric flux field in the frame of the rotor. The DC fieldcan rotate with the rotor. Electrodes of the stator can produce analternating current (AC) charge and corresponding electric fielddistribution that follows the rotor as the rotor rotates. The rotor fluxand the stator flux can travel at the same speed (e.g., a synchronousspeed). Although the rotor flux and the stator flux travel at the samespeed, the angle between the rotor flux vectors and the stator fluxvectors can determine torque by varying the shear in the gap. In someembodiments, the rotor flux may be produced with a permanent electret ormay be separately excited using a power supply connected through arotating shaft power coupling (e.g. brushes and slip rings). In someaspects, synchronous electrostatic machines can be considered to beanalogous to magnetic synchronous machines.

The underlying principles of direct current (DC) electrostatic machinesare similar to those of synchronous electrostatic machines. However, inDC electrostatic machines, the roles of the stator and rotor arereversed from the roles of the stator and the rotor in synchronouselectrostatic machines. Stator electrodes can be excited using DC power,thereby creating a static field. Charge on the rotor, however, can becommutated mechanically. As the rotor spins, charge is commutated by abrushed commutator or a non-brushed commutator such that the charge isaligned with the stator excitation, thereby producing average torque. Insome aspects, DC electrostatic machines can be considered to beanalogous to magnetic DC motors.

Electrostatic hysteresis synchronous machines are analogous totraditional synchronous machines in that rotor and stator flux interactto make torque. However, in electrostatic hysteresis synchronousmachines, ferroelectric materials with an electrostatic hysteresis curveof an electric field versus displacement (e.g., an E-D hysteresis curve)can coat the rotor surface. An E-D hysteresis curve can be a function ofthe electric displacement D for an applied electric field E. In someaspects, an E-D curve for ferroelectric materials can be analogous to aB-H curve for ferromagnetic materials. The slope of an E-D curve for amaterial can represent the permittivity of the material at differentelectric field strengths. The ferroelectric material can be polarizedduring operation and dragged along with the stator flux wave atsynchronous speed. In some aspects, electrostatic hysteresis synchronousmachines can be considered to be analogous to magnetic hysteresissynchronous motors.

Corona machines are different than machines of the other five categoriesexplained above in that the operating principle is electro hydrodynamicflow rather than creating electric shear force via normal and/ortangential fields. Charged particles can be accelerated to form an ionic“wind.” The mechanical interaction of the accelerated particles withrotor and stator structures can create torque. Corona machines can incurhigh electrical losses at macro scales and, therefore, may not besuitable for many applications.

FIGS. 1-8 illustrate various aspects of a variable capacitance machine.A variable capacitance machine can include a shaft, a frame and/orhousing, rotor plates, stator plates, and a dielectric fluid that fillsthe space inside the housing not otherwise occupied by the other parts.The dielectric fluid will be discussed in greater detail below. AlthoughFIGS. 1-8 illustrate embodiments in which rotor electrodes rotate withinstator electrodes (e.g., the rotor electrodes are fixed to a centralshaft with stator electrodes encircling the central shaft), any suitablecapacitance machine may be used. For example, in some embodiments anexternal rotor motor can be used. In such embodiments, stator electrodescan be fixed along an axis, and rotor electrodes can surround the statorelectrodes. That is, the rotor electrodes can rotate around the statorelectrodes.

FIGS. 1A and 1B illustrate cross-sectional views of some shapes of arotor disk or plate in accordance with illustrative embodiments. Therotor plates 100 illustrated in FIGS. 1A and 1B have teeth 105 around anoutside circumference of the plates. FIGS. 2A and 2B illustratecross-sectional views of some shapes of a stator ring/plate inaccordance with illustrative embodiments. The stator plates 200 can haveteeth 205 along an inside circumference of the stator plates 200. In anillustrative embodiment, the rotor plate 100 illustrated in FIG. 1A canbe used with the stator plate 200 illustrated in FIG. 2A. In analternative embodiment, the rotor plate 100 illustrated in FIG. 2B canbe used with the stator plate 200 illustrated in FIG. 2B. In otherembodiments, a combination of rotor plate 100 and stator plate 200shapes can be used. Further, the rotor plate 100 and stator plate 200shapes illustrated in FIGS. 1A, 1B, 2A, and 2B illustrate some examplesof shapes that can be used. In alternative embodiments, any othersuitable shape can be used.

In some embodiments, the teeth 105 of the rotor plate 100 can overlapwith teeth 205 of the stator plate 200 when assembled. The teeth 105 andthe teeth 205 may also be referred to as “electrodes.” FIG. 3A is adiagram illustrating the capacitive relationship between a rotor andstators in accordance with an illustrative embodiment. In alternativeembodiments, additional, fewer, and/or different elements can be used.As shown in FIG. 3A, stator teeth 205 can be located in a plane parallelto the plane of rotor teeth 105. The stator teeth 205 can be positivelycharged and the rotor teeth 105 can be negatively charged. Inalternative embodiments, the rotor teeth 105 can be positively chargedand the stator teeth 205 can be negatively charged. In yet otherembodiments, the rotor teeth 105 and the stator teeth 205 can alternatepolarities over time.

FIG. 3B illustrates the positional relation of rotors and stators inaccordance with an illustrative embodiment. FIG. 3C is an illustrationof an exploded view of a configuration of stators and rotors inaccordance with an illustrative embodiment. In alternative embodiments,additional, fewer, and/or different elements can be used. A plurality ofrotor plates 100 and stator plates 200 can be alternately stackedtogether in a motor. In some embodiments, the number of rotor plates 100and corresponding stator plates 200 can determine, at least in part, theamount of torque and/or power produced by the motor.

In some embodiments, voltages of the stator plates 200 and rotor plates100 can operate at different voltages. Some such embodiments can includevariable capacitance machines. For example, a first portion (e.g., onethird) of the stator plates 200 and a first portion (e.g., one third) ofthe rotor plates 100 can operate together at a first voltage, a secondportion (e.g., one third) of the stator plates 200 and a second portion(e.g., one third) of the rotor plates 100 can operate together at asecond voltage, and a third portion (e.g., one third) of the statorplates 200 and a third portion (e.g., one third) of the rotor plates 100can operate together at a third voltage. In some embodiments, thenominal voltage of the first voltage, the second voltage, and the thirdvoltage can be the same, but can differ in phase. For example, the firstvoltage, the second voltage, and the third voltage can each be out ofphase with one another by 120°. The first portion of the rotor plates100 can interleave with the first portion of the stator plates 200 alonga first portion of a motor shaft, the second portion of the rotor plates100 can interleave with the second portion of the stator plates 200along a second portion of a motor shaft, and the third portion of therotor plates 100 can interleave with the third portion of the statorplates 200 along a third portion of a motor shaft. The first portion ofthe rotor plates 100, the second portion of the rotor plates, and thethird portion of the rotor plates 100 can each be rotationally skewedfrom one another. Similarly, the first portion of the stator plates 200,the second portion of the rotor plates 200, the third portion of therotor plates 200 can each be rotationally skewed from one another. Forexample, each portion can be skewed by one third of the width of teeth105 and/or teeth 205.

The shape of the teeth 105 and the teeth 205 can determine the profilecapacitance waveform. FIGS. 5A and 5B are plots of the capacitancebetween a stator and a rotor versus angular position in accordance withillustrative embodiments. FIGS. 5A and 5B illustrate examples of profilecapacitance waveforms. FIG. 5A illustrates a profile capacitancewaveform for rotor plate 100 of FIG. 1A and stator plate 200 of FIG. 2A.FIG. 5B illustrates a profile capacitance waveform for rotor plate 100of FIG. 1B and stator plate 200 of FIG. 2B.

The profile capacitance waveform can determine the corresponding torquewaveform. The torque waveform form can be the derivative of capacitancewith respect to the position of the rotor plate 100 and the stator plate200. As the rotor plate 100 and stator plate 200 rotate in relation toone another, voltage can be applied to the rotor plate 100 and thestator plate 200 by a power electronic converter or other suitabledevice. In embodiments in which the capacitance varies as a trapezoidalwaveform, such as in FIG. 5A, the applied voltage between the rotorplate 100 and the stator plate 200 by the power electronic converter canbe a pulse or square waveform. In embodiments in which the capacitancevaries as a sinusoidal waveform, such as in FIG. 5B, the applied voltageby the power electronic converter can be a sine wave.

The examples illustrated in FIGS. 5A and 5B represent switched andsynchronous capacitance modes, respectively. As discussed above, suchexamples can be the result of using teeth 105 and teeth 205. Inalternative embodiments, the stator and rotor plates may be stamped insuch a way that spiral lines or veins intersect with one another. FIG.4A illustrates a rotor with radial veins in accordance with anillustrative embodiment. FIG. 4B illustrates a stator with radial veinsin accordance with an illustrative embodiment. In alternativeembodiments, additional, fewer, and/or different elements can be used.In some embodiments, the rotor and stator can be a rotor and a stator asdescribed in co-pending U.S. patent application Ser. No. 14/026,281,which is incorporated by reference herein in its entirety.

A rotor 400 can include a hollow center 405 through which a shaft can beinserted. Hub mounting holes 410 can be used to fix the rotor 400 to theshaft. Slits 415 can be formed in the rotor 400. The slits 415 candefine flexure beams that allow the rotor 400 to flex axially. Spiralsof the rotor 400 can include conducting sections 420 and insulatingsections 425.

A stator 450 can include a hollow center 455 through which a shaft canbe inserted. Plate mounting holes 460 can be used to rotationally fixthe stator 450 such that the stator 450 is stationary with respect to ahousing of the motor. Slits 465 can be formed in the rotor 450. Theslits 465 can allow the stator 450 to flex axially. Spirals of thestator 450 can include conducting sections 470 and insulating sections475.

FIG. 4C is an illustration of an exploded view of a configuration ofstators and rotors with radial veins in accordance with an illustrativeembodiment. In alternative embodiments, additional, fewer, and/ordifferent elements can be used. As shown in FIG. 4C, a plurality ofrotors 400 and stators 450 can be alternately stacked in a motor. Insome embodiments, the direction of the spiral shape of each of therotors 400 and stators 450 can be the same.

FIG. 6 is a cross-sectional view of an illustration of an electrostaticmachine in accordance with an illustrative embodiment. FIGS. 7A and 7Billustrate exterior views of an electrostatic machine in accordance withan illustrative embodiment. FIG. 8 is an illustration of an explodedview of some components of an electrostatic machine in accordance withan illustrative embodiment. In alternative embodiment, additional,fewer, and/or different elements can be used. FIG. 6 is a cut-away viewof a motor 600, FIGS. 7A and 7B are outside views of the motor 600, andFIG. 8 is an exploded view of the motor 600. The motor 600 can include ashaft 605, stator and rotor plates 610, a housing 615, a dielectricfluid recirculation path 620, fluid recirculation path connections 625,and seals 630.

Stators of the stator and rotor plates 610 can be rotationally fixed tothe housing 615. Rotors of the stator and rotor plates 610 can berotationally fixed to the shaft 605. The shaft 605 can rotate within thehousing 615. The housing 615 can be filled with a dielectric fluid. Thedielectric fluid can be recirculated through one or more recirculationpaths 620. When the shaft 605 and, therefore, the rotor plates of thestator and rotor plates 610 are rotating, the dielectric fluid can beforced radially out and through the recirculation paths 620. The use ofrecirculation paths 620 can reduce the fluidic drag on the rotor platesof the stator and rotor plates 610. In some embodiments, therecirculation paths 620 can include a filter, a radiator, a heatexchanger, and/or other elements that can maintain and/or enhanceperformance of the dielectric fluid. The seals 630 can be configured tomaintain fluid integrity of the housing 615 such that the shaft 605 canrotate while the housing 615 remains stationary, and the dielectricfluid can remain within the housing 615.

In some embodiments, rotor plates and/or stator plates can be stampedfrom a sheet of metal. For example, shapes illustrated in FIGS. 1A, 1B,2A, 2B, 4A, and 4B can be stamped. Stamping the rotor plates and/orstator plates can assist in manufacturing and can allow mass productionof the rotor plates and/or stator plates.

Although FIGS. 1-7 illustrate electrostatic machines that use plates aselectrodes, any suitable configuration of electrodes can be used. Forexample, electrostatic machines can be the same as or similar to thosedescribed in U.S. Pat. Nos. 3,094,653, 3,433,981, 6,353,276, and8,779,647, which are incorporated herein by reference in their entirety.

As noted above, a motor, such as motor 600, can convert electricalenergy into rotational kinetic energy. The electrical energy can bethree-phase alternating current (AC) power. In some embodiments, directcurrent (DC) power can be converted into three-phase AC power, which canbe used to power an electrostatic machine, such as electrostaticinduction machines, variable capacitance/elastance machines, synchronouselectrostatic machines, direct current (DC) electrostatic machines, andelectrostatic hysteresis synchronous machines. The DC power can beconverted into three-phase AC power by an inverter. A current sourcedinverter (CSI) can maintain a constant current output to a load, such asan electrostatic machine. A voltage sourced inverter (VSI) can maintaina constant voltage output to the load. In some embodiments, a CSI and/ora VSI may be pulse width modulated for a time-averaged variable output.

Some embodiments can use a VSI and/or a CSI to provide power to anelectrostatic machine. In some embodiments, a CSI can have significantadvantages over a VSI when used with an electrostatic machine. In someinstances, a VSI may not be directly connected to a variable capacitancemachine because, in order to work most efficiently, a VSI can requireinductive properties at AC terminals of the VSI, which the capacitancemachine does not inherently have. However, a CSI can have capacitiveproperties at AC terminals of the CSI in order to work most efficiently,which the capacitance machine does inherently have. Accordingly, in someembodiments, a CSI can be directly connected to an electrostatic machinewithout the use of passive components (e.g., resistors, capacitors,inductors, etc.) between the inverter and the electrostatic machine.

FIGS. 9A and 9B are circuit diagrams of a three-phase inverter and athree-phase machine in accordance with illustrative embodiments. FIGS.9C and 9D are circuit diagrams of a single-phase of a three-phaseinverter in accordance with illustrative embodiments. In alternativeembodiments, additional, fewer, and/or different elements can be used.For example, although FIGS. 9A and 9B illustrate three-phase systems,any suitable multi-phase system can be used, such as two-phase,four-phase, five-phase, ten-phase, etc. FIG. 9A is a circuit diagram ofa three-phase CSI used with a three-phase AC machine, such as anelectrostatic machine, in accordance with an illustrative embodiment.FIG. 9C is a circuit diagram of a single phase of the three-phase CSI ofFIG. 9A. Inverter 900 can be powered by a direct current power source905 and can include a DC link inductor 920 and a plurality of switches910. As illustrated in FIG. 9A, inverter 900 can be used to provide ACpower to a three-phase AC machine 915, which can be an electrostaticmachine. As illustrated in FIG. 9C, inverter 900 can be used to provideone phase of multi-phase AC power to the AC machine 915. The switches910 can be controlled, for example by a controller, in any suitablemanner such that the power of three electrical lines connected to thethree-phase AC machine 915 is three-phase AC. In some embodiments, nopassive components (e.g., resistors, capacitors, inductors, etc.) areused between the inverter 900 and the three-phase AC machine 915.

FIG. 9B is a circuit diagram of a three-phase voltage sourced inverterused with a three-phase AC machine, such as an electrostatic machine, inaccordance with an illustrative embodiment. FIG. 9D is a circuit diagramof a single phase of the three-phase voltage sourced inverter of FIG.9B. Inverter 935 can be powered by a direct current power source 905 andcan include a DC link capacitor 925, a plurality of switches 910, and aplurality of inductors 930. As illustrated in FIG. 9B, inverter 935 canbe used to provide AC power to a three-phase AC machine 915. Asillustrated in FIG. 9D, inverter 935 can be used to provide one phase ofmulti-phase AC power to the AC machine 915. The switches 910 can becontrolled, for example by a controller, in any suitable manner suchthat the power of three electrical lines connected to the three-phase ACmachine 915 is three-phase AC.

FIGS. 9E and 9F are circuit diagrams of a single-phase buck or boostconverter of a three-phase inverter powering a single-phase of athree-phase machine in accordance with illustrative embodiments. Inalternative embodiments, additional, fewer, and/or different elementscan be used. FIGS. 9E and 9F are circuit diagrams of a single-phasevoltage sourced buck or boost converter driving a single phase of athree-phase electrostatic machine, such as a variable capacitanceelectrostatic machine.

FIG. 9E illustrates an electrical power converter 950 that converts DCpower from DC power source 955 into AC power or pulsed DC power forelectrostatic machine 960. The converter 950 can include a DC linkcapacitor 965, switches 975, and an inductor 970. In the embodimentshown in FIG. 9E, switches 975 can include an insulated-gate bipolartransistor (IGBT) and a diode. In alternative embodiments, ametal-oxide-semiconductor field-effect transistors (MOSFET) and a diodecan be used. In yet other embodiments, any suitable switching elementscan be used, such as bipolar junction transistors (BJTs), thyristors,integrated gate commuted thyristors (IGCTs), etc. In some embodiments,switching elements can be used with a diode (e.g., as illustrated inFIG. 9E). In other embodiments, switching elements may not be used witha diode. As shown in FIG. 9E, the converter 950 is a half bridge, whichcan use fewer active semiconductor components than a full bridge. Theconfiguration of the converter 950 illustrated in FIG. 9E can step-down(e.g., “buck”) voltage from the DC power source 955 to the electrostaticmachine 960. The configuration can recover energy back to the DC powersource 955 by stepping-up (e.g., “boosting”) voltage from theelectrostatic machine 960. The stepping-up and stepping-down can bealtered over time.

FIG. 9F illustrates a voltage sourced converter 980 that converts DCpower from DC power source 955 into AC power for electrostatic machine960. The converter 980 can include a DC link capacitor 965, switches975, and an inductor 985. In the embodiment shown in FIG. 9F, switches975 can include an IGBT and a diode. In alternative embodiments, aMOSFET and a diode can be used. As shown in FIG. 9F, the converter 980is a half bridge, which can use fewer active semiconductor componentsthan a full bridge. The configuration of the converter 980 illustratedin FIG. 9F can step-up (e.g., “boost”) voltage from the DC power source955 to the electrostatic machine 960. The configuration can recoverenergy back to the DC power source 955 by stepping-down (e.g.,“bucking”) voltage from the electrostatic machine 960. The stepping-upand stepping-down can be altered over time.

FIGS. 10A and 10B are diagrams of some examples of creating switches inaccordance with illustrative embodiments. FIG. 10A provides someexamples of producing switches of a voltage sourced inverter. FIG. 10Bprovides some examples of producing switches of a current sourcedinverter. In some embodiments, the switches 910 can each be comprised ofone or more semiconductor switches. The semiconductor switches can beable to block voltages greater than 500 Volts (V). In some embodiments,the semiconductor switches can comprise silicon (e.g., crystallinesilicon) as the substrate of the switch. In alternative embodiments, thesemiconductor switches can comprise wide bandgap semiconductors as thesubstrate of the switch, such as silicon carbide (SiC), Gallium Nitride(GaN), diamond, etc. In an illustrative embodiment, each switch 910illustrated in FIGS. 9A-9F can be a silicon carbide semiconductor switchand a diode.

In an illustrative embodiment, each switch 910 illustrated in FIGS. 9Band 9D can be a single silicon carbide semiconductor switch and a diode,as illustrated in diagrams (i) and (ii) of FIG. 10A. As illustrated indiagrams (i) and (iv) of FIG. 10A, in some embodiments, each switch 910can comprise one or more IGBTs with a corresponding diode. Asillustrated in diagrams (ii) and (iii) of FIG. 10A, in some embodiments,each switch 910 can comprise one or more MOSFETs with correspondingdiodes. The diagrams of FIG. 10A can each block voltage in one directionand allow current to flow in either direction. Accordingly, the diagramsof FIG. 10A can be used as switches 910 in voltage sourced inverters. Asillustrated in diagrams (iii) and (iv) of FIG. 10A, multiple switchesillustrated in diagrams (ii) and (i), respectively, can be stacked inseries to increase the voltage blocking capabilities of the switch 910.In some embodiments, additional passive and/or active components may beadded to each switch such that the voltage across each switch is aboutthe same. For example, resistors can be connected in parallel with eachswitch. In alternative embodiments, any suitable combination or use ofdiodes, resistors, capacitors, etc. can be used to equalize voltageacross each switch.

In an illustrative embodiment, each switch 910 illustrated in FIGS. 9Aand 9C can be a single silicon carbide semiconductor switch and a diode,as illustrated in diagrams (i) and (ii) of FIG. 10B. As illustrated indiagrams (i) and (iv) of FIG. 10B, in some embodiments, each switch 910can comprise one or more IGBTs with a corresponding diode and one ormore diodes in series with the IGBTs and their corresponding diodes. Asillustrated in diagrams (ii) and (iii) of FIG. 10B, in some embodiments,each switch 910 can comprise one or more MOSFETs with correspondingdiodes and one or more diodes in series with the MOSFETs and theircorresponding diodes. The diagrams of FIG. 10B can each conduct currentin one direction and block voltage in both directions. Accordingly, thediagrams of FIG. 10A can be used as switches 910 in current sourcedinverters. As illustrated in diagrams (iii) and (iv) of FIG. 10B,multiple switches illustrated in diagrams (ii) and (i), respectively,can be stacked in series to increase the voltage blocking capabilitiesof the switch 910. In some embodiments, additional passive and/or activecomponents may be added to each switch such that the voltage across eachswitch is about the same.

FIGS. 11A and 11B are block diagrams of a capacitive machine drivecontrol system in accordance with illustrative embodiments. Inalternative embodiments, additional, fewer, and/or different elementsmay be used. Also, the use of arrows between elements is not meant to belimiting with respect to the direction of energy flow. FIG. 11A is ablock diagram of an embodiment of controlling a three-phase machinepowered by a VSI power source. A system 1100 can include electricalpower 1105, a VSI 1110, inductors 1115, a machine 1120, mechanical power1125, a voltage sensing feedback 1130, a controller 1135, and a positionsensing line 1140. As illustrated in FIG. 11A, electrical power 1105 canbe input into system 1100 and mechanical power 1125 can be output fromthe system 1100. In alternative embodiments, mechanical power 1125 canbe input into system 1100 and electrical power 1105 can be output fromthe system 1100 (e.g., by using machine 1120 as a generator). Further,although FIG. 11A illustrates a three-phase system, any suitable numberof phases can be used. The machine 1120 can be a multi-phaseelectrostatic machine.

Electrical power 1105 can be input into VSI 1110. In some embodiments,the electrical power 1105 can be direct current power and VSI 1110 canbe a voltage-sourced inverter such as inverter 935. The power of theelectrical connections between the VSI 1110 and the machine 1120 canhave an alternating voltage. Inductors 1115 can be placed in each leg ofthe electrical connections between the VSI 1110 and the machine 1120.

The voltage sensing feedback 1130 can be used in a control loop. Thevoltage sensing feedback 1130 can use one or more sensors to sense avoltage across stator electrodes and rotor electrodes of the machine1120. The voltage sensing feedback 1130 can send a signal to thecontroller 1135 indicating the sensed voltage. The controller 1135 cancompare the sensed voltage to a setpoint voltage. Based on thecomparison, the controller 1135 can indicate a change in the switchingof VSI 1110. The controller 1135 can use a proportional control loop, anintegral control loop, a derivative control loop, or any combinationthereof.

The amount of torque output by the machine 1120 can be dependent uponthe voltage signal applied across the stator electrodes and the rotorelectrodes of the machine 1120. Accordingly, the controller 1135 canmodify the torque output by the machine 1120 by indicating a change inthe switching of the VSI 1110. In some embodiments, the voltage signalsensed by the voltage sensing feedback 1130 can be an alternatingvoltage signal. Similarly, the setpoint voltage can be an alternatingvoltage signal. The indication of a change in switching of the VSI 1110output by the voltage sensing feedback 1130 can include an indication ofa change in frequency, amplitude, phase, etc.

As shown in FIG. 11A, a position sensing line 1140 can be used to inputa position of the shaft of the machine 1120 into the controller 1135.The controller 1135 can use the rotational direction of the shaft of themachine 1120 to determine what voltage should be applied to the machine1120. For example, the position sensing line 1140 can be used to alteramplitude, phase, frequency, etc. of the voltage across the statorelectrodes and the rotor electrodes. In some embodiments, the controller1135 can be controller 1200, discussed in greater detail below.

FIG. 11B is a block diagram of an embodiment of controlling athree-phase machine powered by a CSI power source. A system 1150 caninclude electrical power 1155, a CSI 1160, a machine 1170, mechanicalpower 1175, a voltage sensing feedback 1180, a controller 1185, and aposition sensing line 1190. As illustrated in FIG. 11B, electrical power1155 can be input into system 1150 and mechanical power 1175 can beoutput from the system 1150. In alternative embodiments, mechanicalpower 1175 can be input into system 1150 and electrical power 1155 canbe output from the system 1150 (e.g., by using machine 1150 as agenerator). Further, although FIG. 11B illustrates a three-phase system,any suitable number of phases can be used. The machine 1120 can be amulti-phase electrostatic machine.

Electrical power 1155 can be input into CSI 1110. In some embodiments,the electrical power 1155 can be direct current power and CSI 1110 canbe a current-sourced inverter such as inverter 900. The power of theelectrical connections between the CSI 1110 and the machine 1170 canhave an alternating voltage. The voltage sensing feedback 1180 can beused in a control loop with controller 1185 and position sensing line1190, which can operate as explained above with respect to FIG. 11A.

FIG. 11C is a block diagram of a circuit architecture for powering anelectrostatic machine in accordance with an illustrative embodiment. Inalternative embodiments, additional, fewer, and/or different elementscan be used. A circuit can include a power source 1192, a plurality ofpower converters 1194, inductors 1196, and a machine 1198. As discussedabove, power source 1192 can be a direct current power source. Powerconverters 1194 can be configured to convert power from power source1192 into alternating voltage power for use by the machine 1198. In someembodiments, the power converters 1194 can be configured to convertpower produced by the machine 1198 into electrical power, such as directcurrent electrical power. In the embodiment illustrated in FIG. 11C, athree-phase system is shown. However, any suitable number of phases canbe used. The machine 1198 can be a multi-phase electrostatic machine.

The power converters 1194 can be any suitable power converter, includinga VSI or CSI power converter. As illustrated in FIG. 11A, the powerconverters 1194 can be in parallel with one another and can beconfigured to each provide a power phase to the machine 1198. Inductors1196 are illustrated in each phase of the machine 1198. However, inalternative embodiments, inductors 1196 may not be used.

To scale electrostatic machines up to produce greater than 1 horsepower,medium to high voltage can be used. For example, voltages greater than1000 V can be used between rotor plates and stator plates. Electrostaticinduction machines, variable capacitance/elastance machines, synchronouselectrostatic machines, and electrostatic hysteresis synchronousmachines can use medium to high AC power. Direct current (DC)electrostatic machines and corona machines can use high voltage DCpower. For electrostatic machines that can create greater than onequarter horsepower and less than one megawatt (MW) (e.g., about 1,341horsepower), high voltage power electronic drives can be used. However,high voltage variable frequency AC power sources, which can also besuitable for use with electrostatic machines, are not generallycommercially available.

However, as described above with reference to FIGS. 9A-9F and 10A and10B, various high voltage variable frequency AC power sources can beused. The use of a high voltage variable frequency AC power source canmake electromagnetic machines with greater than one quarter horsepoweroutput practical and useable in commercial and/or industrialapplications.

Electrostatic machines can be used in a variety of applications.Electrostatic machines that can produce less than 1 horsepower can beefficient and compact. However, scaling up the size of electrostaticmachines can produce hurdles in implementation.

In some instances, breakdown of the dielectric fluid can occur in thegap between the surfaces of the stator plate and the rotor plate. Torqueis proportional to the square of the gap electric field. The gapelectric field strength is proportional to the voltage applied acrossthe stator plate and the rotor plate. Breakdown of the dielectric fluidcan lead to arcing between the stator plate and the rotor plate. Arcingevents can reduce the amount of torque that may be developed. Breakdownof the dielectric fluid can pose a problem in electrostatic inductionmachines, variable capacitance/elastance machines, synchronouselectrostatic machines, direct current (DC) electrostatic machines, andelectrostatic hysteresis synchronous machines. In some embodiments, anultra-high vacuum (e.g., less than 10⁻² Torr) can be used within thehousing of the electrostatic machines to prevent arcing. However, thecost of vacuum pumps, bearing vacuum seals, etc. can be costprohibitive. Further, the loss of the relative permittivity material inthe gap between the stator plates and the rotor plates can reduce theeffectiveness of the machine.

A gap displacement field of an electrostatic motor can be thedisplacement field in the gap between the stator plates and the rotorplates. The gap displacement field strength can be proportional to therelative permittivity of the medium filling the gap. Fluids withappreciable relative permittivity (e.g., greater than 7) and/or with lowelectrical conductivity (e.g., 10⁻⁹ Siemens per centimeter (S/cm)) thatare chemically and electrically stable and/or suitable can be used toenhance the efficiency of the machine. Enhancing the gap displacementfield can be beneficial to electrostatic induction machines, variablecapacitance/elastance machines, synchronous electrostatic machines,direct current (DC) electrostatic machines, and electrostatic hysteresissynchronous machines by increasing the electrostatic shear force in thegap for a given voltage.

Accordingly, a fluid that can fill the gap between stator plates androtor plates of an electrostatic machine that has a high permittivity,low conductivity, low viscosity, is chemically stable and suitable formachine components, and is electrically stable and suitable for machinecomponents can be beneficial to electrostatic machines. In someembodiments, beneficial properties for a fill fluid can also includepractical properties such as low toxicity and low flammability. The fillfluid may be a dielectric fluid.

Fluids with a high permittivity fluid can have a molecular structurethat has a high dipole moment. In some instances, strong dipole-dipoleinteractions can generally lead to a higher viscosity and a higherboiling point. Therefore, many fluids with high permittivity also haverelatively high viscosity.

In many instances, high permittivity fluids have inherently highconductivities. Some commercially available high permittivity liquidsthat are 99.5% pure contain too many contaminants to be useful as adielectric fluid within electrostatic machines. The presence of traceamounts of ions, gas, and/or highly mobile molecules can lead tounacceptably high electrical losses and/or premature breakdown.

In some embodiments, liquids with a high permittivity can be purifiedusing suitable techniques. For example, purification may be carried outby dehydration, degasification, or ion removal. In some embodiments, ahigh voltage insulator can have ionic conductivities that are less than10⁻¹² S/cm.

In some embodiments, the dielectric fluid may include ethylenecarbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate,dipropyl carbonate, propylene carbonate, methyl butyrate,γ-butyrolactone, N-methylpyrrolidinone, vinylene carbonate, dioxolane,6-butyrolactone, diethyl ether, or a combination of any two or morethereof.

In some embodiments, the dielectric fluid can have an aromatic structurein which a nitrogen atom is present at a first position in a ring of thearomatic structure and at least one nitrile (CN) group can be asubstituent at a second position. In some embodiments, the dielectricfluid may include a nitrile-substituted heteroaromatic solvent.

In some embodiments, the dielectric fluid can include an acycliccarbonate. An acyclic carbonate has a functional group consisting of acarbon atom that is double bonded to an oxygen atom and single bonded totwo other oxygen atoms. Alkyl groups may be attached to the singlebonded oxygen atoms. The alkyl groups do not link to each other and,therefore, the molecule does not form a ring configuration. Someexamples of acyclic carbonates that can be used as a dielectric fluidinclude dimethyl carbonate, ethyl methyl carbonate, and diethylcarbonate.

In some embodiments, the dielectric fluid can include a cycliccarbonate. A cyclic carbonate has a functional group consisting of acarbon atom that is double bonded to an oxygen atom and single bonded totwo other oxygen atoms. Alkyl groups are attached to the single bondedoxygen atoms. The alkyl groups do link together such that the moleculeforms a ring configuration. Some examples of cyclic carbonates that canbe used as a dielectric fluid include ethylene carbonate, propylenecarbonate, and vinylene carbonate. In some embodiments, the cycliccarbonate can have a moiety that is represented as —OC(O)N. In someembodiments, a methyl group can be attached to the nitrogen atom at the3 position. For example, the dielectric fluid can comprise3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone, and/or3-methyl-1,3-oxazinan-2-one.

In some embodiments, the carbonate can include a sulfone group. Asulfone has a functional group consisting of a sulfur atom that isdouble bonded to two different oxygen atoms and has single bonds to twoseparate alkyl groups. In some embodiments, the sulfone can be acyclic.For example, the dielectric fluid can include dimethyl sulfone, in whichboth alkyl substituents are methyl groups. In alternative embodiments,the sulfone can be cyclic. For example, the dielectric fluid can includesulfolane, in which the alkyl groups are linked together forming a 5member ring. In some embodiments, the dielectric fluid can be dimethylsulfone, sulfolane or a mixture of dimethyl sulfone and sulfolane.

In some embodiments, the dielectric fluid includes propylene carbonate.In some embodiments, the dielectric fluid can be propylene carbonate.The carbonate functional group (—OC(O)C— and/or —OC(O)O—), in cyclicalform, has a high dipole moment of 4.94 debyes (D). In some embodiments,a carbonate functional group with an acyclic form can be used. Propylenecarbonate has a relative permittivity of 64, which is higher than mostother liquids. Propylene carbonate has a relatively low viscosity of2.53 centipoise (cP). Propylene carbonate has a relatively wide range oftemperatures at which it remains in a liquid state (from about −49° C.to about 242° C.). Propylene carbonate is nontoxic, is nonflammable, andis reasonably cost effective. In some embodiments, one or moreco-solvents or additives can be used with propylene carbonate.

In some instances, 99.99% pure propylene carbonate can have an ionicconductivity that can be too high to be suitably efficient. Propylenecarbonate can be commercially available at a purity of 99.99%, but sucha purity can contain about 20 parts per million (ppm) each of propyleneglycol, propylene oxide, water, ionic contaminates, etc. Further,imperfect methods of shipping and/or handling of propylene carbonate canlead to absorption of atmospheric moisture into the propylene carbonate.Thus, in some instances, commercially available propylene carbonate canbe received with a moisture content much higher than 20 ppm.

In some embodiments, propylene carbonate of 99.99% purity or greater maybe used in the electrostatic machines of some embodiments. In someinstances, a suitable purity level of propylene carbonate can depend onthe contaminant. For example, higher purity levels can be used ininstances in which water and ions are contaminants. In another example,relatively lower purity levels can be used for contaminates that aremore innocuous than water and ions. Propylene carbonate at such a puritymay have an ionic conductivity of approximately 10⁻¹⁰ S/cm. Propylenecarbonate at 99.99% purity may be produced using a suitable purificationmethod. Water can be removed from propylene carbonate with 4 angstrom(A) molecular sieves, a plurality of vacuum distillations, and/ordegasification. Such methods can produce a propylene carbonate with apurity level that has a conductivity of less than 10⁻¹¹ S/cm. Forexample, propylene carbonate can be soaked in molecular sieves to reducewater content to be below 2 ppm. Multiple vacuum distillations of thepropylene carbonate may reduce the amount of (e.g., virtually eliminate)propylene glycol, propylene oxide, and/or ionic contaminates. The ionicconductivity can be reduced to a desirable level that limitsself-heating.

In some instances, propylene carbonate is a solvent. Because of its highdipole moment, especially at elevated temperatures, propylene carbonatemay be an effective solvent for plastics (e.g., polyvinyl chloride(PVC)) that contain plasticizer additives. Thus, materials ofconstruction for machines using a dielectric fluid such as propylenecarbonate can be chosen such that contaminates do not leach into thedielectric fluid from other components of the machine. For example, ahousing (or other component) of an electrostatic machine can becomprised of plastics that do not contaminate the dielectric fluid, havea low conductivity, and are mechanically rigid, even when exposed toheated propylene carbonate. Some suitable plastics includepolypropylene, chemical resistant acetal, ultra-high-molecular-weight(UHMW) polyethylene, polytetrafluoroethylene (PTFE), etc.

In alternative embodiments, fluids other than propylene carbonate can beused. For example, hydrofluorocarbons such as a specialty fluid VertrelXF produced by E. I. du Pont de Nemours and Company (DuPont), which is anoncyclic fluorinated hydrocarbon with a chemical formula of C₅H₂F₁₀,have physical properties that can be suited for a dielectric fluid in anelectrostatic machine. In some embodiments, such as those with smallelectrode gaps (e.g., less than 0.38 mm), Vertrel has an inherentbreakdown voltage of greater than 20 kilovolts per millimeter (kV/mm).In some embodiments, Vertrel can be suitably pure as commerciallyavailable. For example, conductivities of about 10⁻¹² Siemens percentimeter (S/cm) can be commercially available and can be suitable foruse in an electrostatic machine. In such an example, a solvent forpurification may not be required. The viscosity of Vertrel is relativelylow (0.67 cP). Vertrel is nonflammable and has a low toxicity. Inalternative embodiments, the dielectric fluid can comprise (or can be)other hydrofluorocarbons, such as Novec 7100 produced by 3M. Novec 7100is a noncyclic fluorinated hydrocarbon with a chemical formula C₄F₉OCH₃.Novec 7100 has properties similar to those of Vertrel.

However, Vertrel has a relative permittivity of 7.1, which can generateless torque in an electrostatic machine than fluids with a higherpermittivity. Vertrel has a boiling point of 55° C., and, therefore, canbe volatile and problematic for elevated working temperatures. In someembodiments, Vertrel can be used as a dielectric fluid in anelectrostatic machine. In alternative embodiments, Vertrel can be usedas a co-solvent with a fluid that has a relatively high permittivity.

In some embodiments, one or more fluids can be mixed together to producea dielectric fluid to be used in an electrostatic machine. The mixturecan have a combination of properties that is better than any of itsconstituent fluids. For example, a mixture of a high permittivity fluidwith a low viscosity fluid can have a relatively high permittivity and arelatively low viscosity. In general, some high permittivity fluids arealso highly viscous and conductive. In some embodiments, such highpermittivity fluids can be mixed with a low permittivity fluid that haslow viscosity and low conductivity. The resulting mixture can have abalance of physical properties that can be better suited as a dielectricfluid within an electrostatic machine.

In some embodiments, a propylene carbonate-Vertrel mixture can be used.For example, some mixed dielectric fluids can have a weight ratio ofpropylene carbonate to Vertrel of 60% to 40%, 70% to 30%, 80% to 20%,etc. or any ratio therein. A propylene carbonate-Vertrel mixture wherethe component ratio maximizes the combination of permittivity andbreakdown voltage can be used for an application in which high torqueproduction is the top priority. In alternative embodiments, a propylenecarbonate-Vertrel mixture can be tailored to minimize the conductivityof the fluid for an application in which electrical efficiency of theelectrostatic machine is most important. In yet other embodiments, adifferent propylene carbonate-Vertrel mixture can be used to create adielectric fluid mixture that has appropriate properties for thespecific application.

In some embodiments, ethylene carbonate can be used as a dielectricfluid. Ethylene carbonate is a cyclic carbonate that has similarproperties as propylene carbonate. However, small structural differencesbetween ethylene carbonate and propylene carbonate can give ethylenecarbonate a higher permittivity than propylene carbonate. The relativepermittivity of ethylene carbonate is close to 90, which is about 40%higher than the permittivity of propylene carbonate. The highpermittivity of ethylene carbonate allows more torque to be generated inan electrostatic machine when compared to propylene carbonate.

Ethylene carbonate possesses other properties that may not be ideal foruse as a dielectric fluid in some embodiments. The relatively highmelting point of ethylene carbonate (e.g., 37° C.) can preclude ethylenecarbonate from being the sole dielectric fluid in some embodiments of anelectrostatic machine. However, in some embodiments, the dielectricfluid can be operated at elevated temperature applications that allowthe ethylene carbonate to be a liquid.

In some embodiments, ethylene carbonate can be mixed with other fluids,such as propylene carbonate, to create a liquid solution at roomtemperature with high permittivity. For example, a mixture of 70% to 80%of ethylene carbonate and 30% to 20% of propylene carbonate can be used.Although ethylene carbonate is commercially available at 99.99% purity,additional purification can be performed to increase the suitablenessfor electrostatic machines. Any suitable method of purification can beused.

In some embodiments, a passivation layer can be created betweenelectrodes (e.g., rotor plates and stator plates) and the dielectricfluid. In some instances, high permittivity fluids, such as propylenecarbonate, can be thermodynamically unstable in a high electric filed.Such fluids can produce a gas that can lower the breakdown voltage,thereby leading to arcing between the electrodes. For example, propylenecarbonate can be reduced at a negative electrode to produce propylenegas, and can be oxidized at the positive electrode to produce carbondioxide gas.

In some embodiments, a passivation layer can be formed on the surface ofthe electrodes to reduce and/or eliminate gas formation by creating abarrier that hinders electron transfer between the electrode and thefluid. For example, a propylene carbonate based fluid including 6% byvolume ethylene sulfite and 0.2% by volume water can be used as adielectric fluid within an electrostatic machine to create a passivationlayer. Ethylene sulfite can form an effective passivation layer on thenegative electrode in propylene carbonate based solutions. Dopingpropylene carbonate with trace amounts of water can form an effectivepassivation layer on positively charged electrodes. For example, thebreakdown voltage of a machine without a passivation layer can be 4.7kV/mm. With the addition of a passivation layer on the electrodes of themachine, the breakdown voltage can be increased to 9.9 kV/mm. Inalternative embodiments, any suitable fluid can be used to create adielectric fluid for forming a passivation layer on the electrodes.Although ethylene sulfite and water are used in the example above, inalternative embodiments, any suitable additives can be used withpropylene carbonate to form a passivation layer on the electrodes. Forexample, a mixture of 99% by weight propylene carbonate and 1% by weightadditives can be used. In other examples, 98.5%, 98%, 95%, 90%, 80%,etc. by weight propylene carbonate can be used.

In some embodiments, a first dielectric fluid can be used to create apassivation layer (e.g., a propylene carbonate based fluid including 6%by volume ethylene sulfite and 0.2% by volume water) and a seconddielectric fluid can be used while operating the electrostatic machine(e.g., high purity propylene carbonate). The rotor electrodes and statorelectrodes can be immersed in a first dielectric fluid. The firstdielectric fluid can fill a gap between stator electrodes and rotorelectrodes. In some embodiments, a DC voltage can be applied across thestator electrodes and the rotor electrodes. The first dielectric fluidcan react with surfaces of the stator electrodes and rotor electrodes,thereby forming a passivation layer on the electrodes. The firstdielectric fluid can be removed from the electrodes. In some instances,the stator electrodes and rotor electrodes can be rinsed with distilledwater and dried. In some embodiments, the passivation layer can beproduced on the stator electrodes and rotor electrodes while theelectrodes are outside of a housing of the electrostatic machine. Thestator electrodes and the rotor electrodes can be assembled and placedin the housing. The housing of the electrostatic machine can be filledwith the second dielectric fluid. The electrostatic machine can be runas intended with the second dielectric fluid.

In alternative embodiments, any suitable method can be used to provide apassivation layer on electrodes of an electrostatic machine. Forexample, the electrodes can be covered with carbon (e.g., diamond),silver, ceramic (e.g., BaTiOP₃), etc. In yet other embodiments, nopassivation layer may be used. In such embodiments, circulation of thedielectric fluid can be sufficient to prevent gas from building up onthe electrodes.

Several factors can effect efficiency and power output of electrostaticmachines. The force density between stator plates and rotor platesincreases with the square of the applied electric field. Such arelationship can be seen in Coulombs law, discussed above. Thus, theapplied electric field can be an important factor in creating anefficient and useful electrostatic machine. The permittivity of a fluidcan be defined by the maximum electric field that can be applied beforebreakdown (e.g., arcing). Many factors can affect permittivity of afluid including the gap size between rotor plates and stator plates, thematerial of the rotor plates and the stator plates, surface condition ofthe rotor plates and stator plates, geometry of the rotor plates andstator plates, liquid molecular structure and presence of impurities inthe dielectric fluid, the nature of applied voltage, temperature,pressure, and uniformity of the electric field. One or more of suchfactors can be influenced to maximize permittivity of the fluid.

In some embodiments, increasing the distance between the electrodes(e.g., rotor plates and stator plates) can produce a significant drop inthe permittivity. Experimentation with propylene carbonate confirmedthat decreasing the gap improves the breakdown voltage until the gap isreduced to below 0.30 millimeters (mm). The permittivity can be largelyindependent of gap for gap sizes smaller than 0.30 mm. Accordingly, insome embodiments gaps between stator plates and rotor plates in machinescan be about 0.30 mm.

Different metals can differ in their ability to donate or receiveelectrons. Accordingly, the proper pairing of electrodes can producespace-charge effects that can alter the uniformity of the appliedelectric field and, consequently, can affect the permittivity and ionicconductivity. In some embodiments, aluminum can be used for thenegatively charged plates and stainless steel can be used for thepositively charged plates with propylene carbonate as the dielectricfluid. Such a configuration can produce a force density of 10 pounds persquare inch (psi). By changing the material of the positively chargedplates to be aluminum, a force density of 4.5 psi can be produced.Accordingly, in some embodiments, materials of construction for therotor plates can be different than materials of construction for thestator plates.

In some embodiments, one or more additives can be added to thedielectric fluid. For example, a small amount (e.g., 10% by volume) of2-pyridine carbonitrile can be added to propylene carbonate. Such acombination has been discovered by experimentation to produce thegreatest force density, which was measured at 11.8 psi. The improvedefficacy of this mixture can be due to space-charge effects. Theimproved efficacy can also (or alternatively) be the result of a largecross sectional area and resonance stability, which makes thecombination of fluids an effective electron absorber.

Electrostatic machines that are compact and easy to manufacture canincrease the utility of such machines. In some instances, compactpackaging of an electrostatic machine can be difficult because of thehigh voltage clearances required of the internal parts (e.g., statorplates and rotor plates) with respect to the housing. Further, sealscapable of maintaining a high vacuum within the housing can bemechanically challenging. Because of the clearances needed betweenstator plates and rotor plates and maintenance of high vacuum, in someinstances, electrostatic machines can be bulky and oversized.

However, electrostatic machines that use a dielectric fluid in the gapbetween the stator plates and the rotor plates may not need a highvacuum within the housing of the machine. Accordingly, the housing canbe more compact and thinner, complicated vacuum seals may not be used,and a vacuum pump and associated hoses may not be used. Further, byusing a dielectric fluid between the gaps of the stator plates and therotor plates, the clearances between the stator plates and the rotorplates can be reduced, thereby reducing the size of the machine. Thus,by using a dielectric fluid, in some embodiments, the power density ofelectromagnetic machines can be increased.

Additionally, use of a dielectric fluid can be used as a heat transfermedium. Electrical and mechanical losses (e.g., inefficiencies) cancreate heat. Excessive heat can further reduce the efficiency ofelectrostatic machines. As discussed above, in some embodiments, anelectrostatic machine can include one or more recirculation paths thatcan flow dielectric fluid around various parts of the electrostaticmachine. Thus, the dielectric fluid can transfer heat from hottercomponents (e.g., stator plates, rotor plates, shafts, bearings, etc.)to cooler components (e.g., housing). Further, the one or morerecirculation paths can include one or more heat exchangers configuredto dissipate heat from the dielectric fluid.

As mentioned above, various aspects of an electrostatic motor system canbe controlled, monitored, communicated with, etc. with one or morecontrollers. FIG. 12 is a block diagram of a controller in accordancewith an illustrative embodiment. In alternative embodiments, additional,fewer, and/or different elements may be used. A controller 1200 caninclude a processor 1205, a memory 1210, an input and/or output (I/O)transceiver 1215, a communications transceiver 1220, a power source1230, and a user interface 1225. An electrostatic motor system can useone or more controllers 1200 to control and/or monitor variouscomponents and/or sensors of the flywheel energy storage system.

In some embodiments, controller 1200 can include processor 1205.Processor 1205 can be configured to carry out and/or cause to be carriedout one or more operations described herein. Processor 1205 can executeinstructions as known to those skilled in the art. The instructions maybe carried out by one or more special purpose computers, logic circuits(e.g., programmable logic circuits (PLC)), and/or hardware circuits.Thus, processor 1205 may be implemented in hardware, firmware, software,or any combination of these methods. The term “execution” is the processof running an application or the carrying out of the operation calledfor by an instruction. The instructions may be written using one or moreprogramming language, scripting language, assembly language, etc.Processor 1205 executes an instruction, meaning that it performs theoperations called for by that instruction. Processor 1205 operablycouples with memory 1210, communications transceiver 1220, I/Otransceiver 1210, power source 1230, user interface 1225, etc. toreceive, to send, and to process information and to control theoperations of the controller 1200. Processor 1205 may retrieve a set ofinstructions from a permanent memory device such as a read-only memory(ROM) device and copy the instructions in an executable form to atemporary memory device that is generally some form of random accessmemory (RAM). Controller 1200 may include a plurality of processors thatuse the same or a different processing technology. In an illustrativeembodiment, the instructions may be stored in memory 1210.

In some embodiments, controller 1200 can include memory 1210. Memory1210 can be an electronic holding place or storage for information sothat the information can be accessed by processor 1205 as known to thoseskilled in the art. Memory 1210 can include, but is not limited to, anytype of random access memory (RAM), any type of read-only memory (ROM),any type of flash memory, etc. such as magnetic storage devices (e.g.,hard disk, floppy disk, magnetic strips, etc.), optical disks (e.g.,compact disk (CD), digital versatile disk (DVD), etc.), smart cards,flash memory devices, etc. Controller 1200 may have one or morecomputer-readable media that use the same or a different memory mediatechnology. Controller 1200 may have one or more drives that support theloading of a memory medium such as a CD, a DVD, a flash memory card,etc.

In some embodiments, controller 1200 can include a communicationstransceiver 1220. Communications transceiver 1220 can be configured toreceive and/or transmit information. In some embodiments, communicationstransceiver 1220 can communicate information via a wired connection,such as an Ethernet connection, one or more twisted pair wires, coaxialcables, fiber optic cables, etc. In some embodiments, communicationstransceiver 1220 can communicate information via a wireless connectionusing microwaves, infrared waves, radio waves, spread spectrumtechnologies, satellites, etc. Communications transceiver 1220 can beconfigured to communicate with another device using cellular networks,local area networks, wide area networks, the Internet, etc. In someembodiments, one or more of the elements of controller 1200 communicatevia wired or wireless communications.

In some embodiments, controller 1200 can include an I/O transceiver1215. The I/O transceiver 1215 can be configured to communicate withand/or receive information from one or more sensors, devices, etc. TheI/O transceiver 1215 can further be configured to transmit informationto switches of a power converter (e.g., switches 910, switches 975,etc.). The I/O transceiver 1215 can be configured to receive informationfrom one or more sensors, such as temperature sensors, pressure sensors,power sensors, voltage sensors, current sensors, torque sensors, etc.The I/O transceiver 1215 can be configured to send and transmit discreteinformation, analog information, digital information, etc. The I/Otransceiver can include multiple cards and/or communication ports.

In some embodiments, controller 1200 can include power source 1230.Power source 1230 can be configured to provide electrical power to oneor more elements of controller 1200. In some embodiments, power source1230 can include an alternating power source, such as available linevoltage (e.g., 120 Volts alternating current at 60 Hertz in the UnitedStates). Power source 1230 can include one or more transformers,rectifiers, etc. to convert electrical power into power useable by theone or more elements of controller 1200, such as 1.5 V, 8 V, 12 V, 24 V,etc. Power source 1230 can include one or more batteries.

In some embodiments, controller 1200 can include user interface 1225.User interface 1225 can be configured to receive and/or provideinformation from/to a user. User interface 1225 can be any userinterface known in the art. User interface 1225 can be an interface forreceiving user input and/or machine instructions for entry intocontroller 1200 as known to those skilled in the art. User interface1225 may use various input technologies including, but not limited to, akeyboard, a stylus and/or touch screen, a mouse, a track ball, a keypad,a microphone, voice recognition, motion recognition, disk drives, remotecontrollers, input ports, one or more buttons, dials, joysticks, etc. toallow an external source, such as a user, to enter information intocontroller 1200. User interface 1225 can be used to navigate menus,adjust options, adjust settings, adjust display, etc. User interface1225 can be configured to provide an interface for presentinginformation from controller 1200 to external systems, users, or memory.For example, user interface 1225 can include an interface for a display,a printer, a speaker, alarm/indicator lights, a network interface, adisk drive, a computer memory device, etc. User interface 1225 caninclude a color display, a cathode-ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light-emitting diode (OLED)display, etc.

In an illustrative embodiment, any of the operations described hereincan be implemented at least in part as computer-readable instructionsstored on a computer-readable memory. Upon execution of thecomputer-readable instructions by a processor, the computer-readableinstructions can cause a node to perform the operations.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable”, to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.” Further, unlessotherwise noted, the use of the words “approximate,” “about,” “around,”etc., mean plus or minus twenty percent.

The foregoing description of illustrative embodiments has been presentedfor purposes of illustration and of description. It is not intended tobe exhaustive or limiting with respect to the precise form disclosed,and modifications and variations are possible in light of the aboveteachings or may be acquired from practice of the disclosed embodiments.It is intended that the scope of the invention be defined by the claimsappended hereto and their equivalents.

What is claimed is:
 1. An electrostatic machine comprising: a shaftconfigured to rotate about an axis; a rotor electrode and a statorelectrode separated by a gap and forming a capacitor, wherein the rotorelectrode is fixed to the shaft; a housing configured to enclose therotor electrode, the stator electrode, and a portion of the shaft,wherein the stator electrode is fixed to the housing; and a dielectricfluid that fills a void defined by the housing, the rotor electrode, andthe stator electrode, wherein the dielectric fluid comprises a compoundhaving a carbonate moiety; a nitrile substituted heteroaromatic solventa compound having a cyclic structure and a moiety represented as—OC(O)N—; a fluorinated acyclic hydrocarbon; a compound having asulfonyl group; methyl butyrate, γ-butyrolactone, N-methylpyrrolidinone,vinylene carbonate, dioxolane, δ-butyrolactone, diethyl ether, or amixture of any two or more thereof.
 2. The electrostatic machine ofclaim 1, wherein the dielectric fluid comprises a carbonate moiety. 3.The electrostatic machine of claim 1, wherein the dielectric fluidcomprises a nitrile substituted heteroaromatic solvent.
 4. Theelectrostatic machine of claim 3, wherein the dielectric fluid comprises2-pyridinecarbonitrile.
 5. The electrostatic machine of claim 4, whereinthe dielectric fluid comprises about 10 wt % 2-pyridinecarbonitrile andabout 90 wt % propylene carbonate.
 6. The electrostatic machine of claim1, wherein the dielectric fluid comprises a cyclic structure, and amoiety represented as —OC(O)N—.
 7. The electrostatic machine of claim 6,wherein the dielectric fluid comprises 3-methyl-2-oxazolidinone,3-ethyl-2-oxazolidinone, or 3-methyl-1,3-oxazinan-2-one.
 8. Theelectrostatic machine of claim 1, wherein the dielectric fluid comprisesa fluorinated acyclic hydrocarbon.
 9. The electrostatic machine of claim8, wherein the dielectric fluid comprises C₅H₂F₁₀.
 10. The electrostaticmachine of claim 1, wherein the dielectric fluid comprises a sulfonylgroup.
 11. The electrostatic machine of claim 1, wherein the dielectricfluid comprises dimethyl sulfone, sulfolane, or a mixture thereof. 12.The electrostatic machine of claim 1, wherein the dielectric fluidcomprises ethylene carbonate, dimethyl carbonate, diethyl carbonate,ethylmethyl carbonate, dipropyl carbonate, propylene carbonate, methylbutyrate, γ-butyrolactone, N-methylpyrrolidinone, vinylene carbonate,dioxolane, 6-butyrolactone, diethyl ether, or a mixture of any two ormore thereof.
 13. The electrostatic machine of claim 1, wherein thedielectric fluid comprises propylene carbonate having a purity ofgreater than 99%.
 14. The electrostatic machine of claim 1, wherein therotor electrode and the stator electrode each comprise a passivationlayer formed using a second dielectric in the gap between the rotorelectrode and the stator electrode, and wherein the second dielectricfluid comprises less than 99 wt % propylene carbonate.
 15. Theelectrostatic machine of claim 14, wherein a direct current voltage isapplied across the rotor electrode and the stator electrode to form thepassivation layer.
 16. The electrostatic machine of claim 1, furthercomprising a current sourced inverter configured to convert directcurrent power into alternating current power via a plurality ofswitches, wherein the current sourced inverter is configured to providethe alternating current power across the rotor electrode and the statorelectrode, and wherein no passive electrical components are electricallyconnected between the rotor electrode, the stator electrode, and theplurality of switches.
 17. The electrostatic machine of claim 1, furthercomprising a voltage sourced inverter configured to convert directcurrent power into alternating current power via a plurality ofswitches, wherein a plurality of inductors are electrically connectedbetween the rotor electrode, the stator electrode, and the plurality ofswitches.
 18. The electrostatic machine of claim 1, wherein the rotorelectrode comprises a rotor plate, and wherein the stator electrodecomprises a stator plate, and wherein the rotor plate and the statorplate are parallel.
 19. The electrostatic machine of claim 18, whereinthe rotor plate comprises a plurality of teeth around a periphery of therotor plate, wherein the stator plate comprises an annulus with aplurality of teeth extending from an inside circumference of theannulus, and wherein the teeth of the rotor plate and the teeth of thestator plate form the capacitor.
 20. The electrostatic machine of claim1, wherein the housing comprises at least one of polypropylene, chemicalresistant acetal, ultra-high-molecular-weight (UHMW) polyethylene, andpolytetrafluoroethylene (PTFE).